The invention relates to a multi-stage diaphragm suction pump, comprising at least two pump chambers, each having a fluid inlet having at least one inlet valve, and a fluid outlet having at least one outlet valve, and comprising a suction line, which connects the fluid inlets of the pump chambers, wherein successive pump chambers are each connected to one another by means of at least one connection line in such a way that, when a differential pressure in the suction line is reached/exceeded, the diaphragm pump changes from parallel operation of the pump chambers thereof to an operating mode of said pump chambers that is at least also serial, and wherein at least one check valve, which opens to the downstream pump stage, is interposed in each of the inflow and outflow regions of the at least one connection line.
During the evacuation of an autoclave, for example, the desire is, on the one hand, for a high delivery rate and, on the other hand, for a good ultimate vacuum. The high delivery rate is achieved by connecting the heads in parallel, while the good ultimate vacuum is achieved by multi-stage operation, i.e. by connection in series. In many applications, especially in laboratories, a low ultimate pressure is required, and this can only be achieved with a multi-stage arrangement.
WO 2004/088138 has already disclosed a micro vacuum pump which has two pump chambers, each delimited by an oscillating pump diaphragm. Each of these pump chambers has a fluid inlet having an inlet valve, and a fluid outlet having an outlet valve, wherein a suction line, which connects the fluid inlets of the pump chambers, and a pressure line, which connects the fluid outlets, are provided. The pump chambers are connected to one another by means of a connection line in such a way that, when a defined differential pressure in the suction line is reached and exceeded, the known micro vacuum pump changes from parallel operation of the pump chambers thereof to serial operation of said pump chambers. A check valve, which opens to the downstream pump stage, is interposed both in the inflow region and in the outflow region of the connection line. In order to reduce the outlay involved in the production of the known diaphragm suction pump, the check valves interposed in the connection line are similar in size to the inlet and outlet valves of the two pump chambers. Accordingly, the dimensions of the connection line segment provided between one of the check valves, on the one hand, and the adjacent pump chamber, on the other hand, are also similar. In order nevertheless to be able to pass the fluid flow initially via the parallel-connected inlet and outlet valves in the starting phase of a pumping operation, a restrictor which loses its restricting action only when an appropriate pressure difference and a reduced pump output are reached is interposed in the connection line.
At the beginning of the suction process, the known micro vacuum pump adopts a configuration for parallel operation of the pump chambers thereof because the restrictor provided in the connection line has the effect that the system can initially configure itself more easily for parallel operation, owing to the absence of hindrances to air circulation at that point in time. As soon as this configuration for parallel operation enters the ultimate vacuum range and the pressure difference in the suction line therefore reaches a maximum, it is much easier for the fluid to flow through the restrictor situated in the connection line and, as a result, it is simultaneously also configured for serial operation of the pump chambers thereof in order then to achieve a maximum possible ultimate vacuum.
However, the disadvantage is that the check valves of the known diaphragm pump are similar in size to the inlet and outlet valves and that the connection line segments which are provided between the check valves have a correspondingly large clear line cross section, with the result that there is a correspondingly large dead space in these line segments, which has an effect on the achievable ultimate vacuum of the known diaphragm suction pump and has a negative effect on the changeover point between parallel and serial operation.
In order to achieve as high as possible an ultimate vacuum within the shortest possible time and in order to approximate to the optimum changeover point between parallel and serial operation, another solution already adopted is to provide a multi-stage diaphragm pump in which the check valves provided in the inflow and in the outflow region of the connection line(s) are made smaller than the inlet and outlet valves of the pump chambers, and said check valves are each assigned a connection line segment which is open toward the adjacent pump chamber and has a smaller clear line cross section than the inlet and outlet valves (cf. DE 10 2007 057 945 A1). From a comparison of FIGS. 1 and 2 and the 90° sectional representation in FIG. 4 of DE 10 2007 057 945 A1, it will be clear that the inlet and outlet openings of the connection lines are arranged in the crank axis plane in this known diaphragm pump too. In the at least one connection line, which connects the pump chambers thereof to one another, this known diaphragm pump has check valves both on the inflow side and on the outflow side, and these valves are of considerably smaller dimensions than the inlet and outlet valves of said pump chambers. Since the moving valve element of these check valves can thus also have lower moving masses and accordingly can respond more quickly, an approximation to the optimum changeover point between parallel and serial operation is significantly promoted. Since the connection line only takes effect in the region of the optimum changeover point and since the connection lines have only to cope with comparatively small delivery rates in this pumping phase, the clear cross section of the connection lines can be made comparatively small in comparison with the suction and the pressure line. This also enables the check valves provided in the at least one connection line to be embodied with a very small flow cross section and with a correspondingly small diameter in comparison with the suction and pressure valves. Owing to the low mass of the moving valve or shutoff element of the check valves, these check valves can thus respond quickly when the suction and pressure valves close, and thereby prevent the diaphragm pump already known from DE 10 2007 057 945 A1 from delivering only an inadequate output or none at all in a transitional range of the pressure differences. Since each of the check valves is assigned a line segment leading to the adjacent pump chamber which has a significantly smaller clear line cross section than the inlet and outlet valves, the dead space remaining between a check valve, on the one hand, and the adjacent pump chamber, on the other hand, can be kept so small that even the production of a very low ultimate vacuum as possible to be produced in as short a time as possible by comparatively simple technical means.
DE 10 2006 043 159 B3 has already disclosed a two-stage vacuum pump for superheated steam, which has diaphragms acting in opposition as pumping members. The two pump chambers have inlets and outlets which are fitted with check valves and are each connected to one another in parallel by lines. The pump chambers are connected by means of a control line, which contains a check valve arrangement. In order to produce a high ultimate vacuum as quickly as possible, DE 10 2006 043 159 B3 makes provision for the valve members of the check valve arrangement associated with the connection line to have a significantly lower mass than the valve members of the check valves associated with the inlets and outlets of the pump chambers.
The pressure- and the suction-side openings of the connection line in the diaphragm pump already known from DE 10 2006 043 159 B3 are also provided approximately centrally between the pressure and suction valves of the pump chambers, on a line arranged axially parallel with the axis of rotation of the connecting rod. Since the working diaphragm which rolls on the pump chamber wall reaches the openings of the connection line approximately only in the end position thereof in each pump chamber, leakage flows can escape via said openings of the connection line, exerting an unfavorable effect on the performance of said diaphragm pumps.
The situation revealed by FIGS. 2a and 2b in cited document DE 10 2006 043 159 B3 is no different. In FIGS. 2a and 2b of DE 10 2006 043 159 B3 namely, only the fluid inlets and outlets connected to the pump chambers are shown in longitudinal section in the region of the check valves 1.5 and 1.6 thereof, while the suction- and pressure-side openings of the connection line connecting the pump chambers, which openings are arranged outside the section plane, are not shown and are not visible. These openings are instead visible in the region of the control valves 1.7 and 2.7 thereof in the partially cross-sectioned plan view in FIG. 3. In this figure, the suction- and pressure-side openings of the connection line connecting the pump chambers to one another are also provided approximately centrally between the pressure and the suction valves of the pump chambers, on a line arranged axially parallel with the axis of rotation of the connecting rod.
In the diaphragm pumps already known from WO 2004/088138 and from DE 10 2007 057 945 A1, the pressure- and the suction-side openings of the connection lines are provided approximately centrally between the pressure and the suction valves of the pump chambers, on a line arranged axially parallel to the axis of rotation of the connecting rod. Since the working diaphragm which rolls on the pump chamber wall reaches the openings of the connection lines approximately only in the end position thereof in each pump chamber, leakage flows can escape via said openings of the connection lines, exerting an unfavorable effect on the performance of said diaphragm pumps.